1. Field of the Invention
The present invention relates to a linear image sensor including a photoelectric converting device line in which a photoelectric converting device is linearly provided on a semiconductor, and more particularly to a suitable linear image sensor for color photographing including a plurality of photoelectric converting device lines.
2. Description of the Related Art
A linear image sensor to be utilized in various apparatuses such as a facsimile, an electronic copying machine, an image scanner and a bar code reader has an image pick-up section formed on a semiconductor substrate. The image pick-up section includes a photoelectric converting device line in which a photoelectric converting device such as a photodiode is provided almost linearly and an electric charge transfer section formed close to the photoelectric converting device line. The electric charge transfer section includes an electric charge transfer channel for transferring a signal charge detected by the photoelectric converting device and a plurality of electric charge transfer electrodes for controlling a signal charge transfer. The signal charge transferred by the electric charge transfer section is sent to an output section such as a floating diffusion amplifier and is output as a voltage signal.
In a linear image sensor for color image pick-up, color filters of red, green and blue are formed on the photoelectric converting devices and the photoelectric converting devices detect signal charges corresponding to a red color, a green color and a blue color, respectively.
FIG. 36 shows a schematic structure according to an example of the image pick-up section of a conventional linear image sensor for color image pick-up. A linear image sensor in FIG. 36 is provided with three photodiode lines 511, 512 and 513 having an almost rectangular photodiode 500 arranged linearly, and electric charge transfer sections 521, 522 and 523 are juxtaposed with the photodiode lines 511, 512 and 513, respectively. Output sections 531, 532 and 533 including a floating diffusion amplifier are formed on the ends of the electric charge transfer sections 521, 522 and 523, and a voltage corresponding to a signal charge detected by the photodiode 500 is output from each of the output terminals 541, 542 and 543.
The photodiode lines 511, 512 and 513 output signals corresponding to a red light, a green light and a blue light, respectively. More specifically, a red filter (not shown) is provided in each photodiode forming the photodiode line 511, a green filter (not shown) is provided in each photodiode forming the photodiode line 512 and a blue filter (not shown) is provided in each photodiode forming the photodiode line 513.
Accordingly, a signal shown in FIG. 37(a) is output from each of the output terminals 541, 542 and 543, and therefore, can be utilized as a color image pick-up signal shown in FIG. 37(b) after an AD conversion and other processings are carried out. The symbols R1, R2, . . . , Rn, G1, G2, . . . , Gn, B1, B2, . . . , Bn in FIG. 37 indicate signals detected by photodiodes having the symbols R1, R2, . . . , Rn, G1, G2, . . . , Gn, B1, B2, . . . , Bn in FIG. 36 and so is the following description.
In the linear image sensor shown in FIG. 36, however, it is necessary to provide the electric charge transfer sections 521 and 522 between the photodiode lines 511 and 512 and between the photodiode lines 512 and 513. For this reason, a spacing between the photodiode lines 511, 512 and 513 cannot be reduced. In order to pick up an image having a high resolution, therefore, precision in a position in such a direction (hereinafter referred to as a subscanning direction in some cases) as to cross the direction of arrangement of the photodiode lines 511, 512 and 513 (hereinafter referred to as a main scanning direction in some cases). The precision in the subscanning direction depends on the mechanical precision of a subscanning mechanism and it is generally hard to inexpensively obtain a mechanism with high precision.
FIG. 38 is a view showing a schematic structure according to another example of the image pick-up section of a conventional linear image sensor for color image pick-up. The linear image sensor shown in FIG. 38 is provided with two photodiode lines 611 and 612 having an almost rectangular photodiode 600 arranged linearly. The photodiode lines 611 and 612 are provided close to each other, and electric charge transfer sections 621 and 622 are provided on the outside of the photodiode lines 611 and 612. Moreover, output sections 631 and 632 including a floating diffusion amplifier are formed on the ends of the electric charge transfer sections 621 and 622 and a voltage corresponding to a signal charge detected by the photodiode 600 is output from each of the output terminals 641 and 642.
A red filter and a blue filter (not shown) are alternately provided in each photodiode forming the photodiode line 611, and a green filter (not shown) is provided in each photodiode forming the photodiode line 612.
Accordingly, a signal shown in FIG. 39(a) is output from each of the output terminals 641 and 642, and therefore, can be utilized as a color image pick-up signal shown in FIG. 39(b) by the execution of an operation for a color signal after an AD conversion and other processings are carried out.
In the linear image sensor shown in FIG. 38, the photodiode lines 611 and 612 are provided close to each other. Therefore, the mechanical precision of a subscanning mechanism is not always required. However, it is hard to provide horizontal transfer electrodes H1, H2 . . . . More specifically, if the number of the photodiode lines is increased to enhance a detection sensitivity, the electric charge transfer section is provided in the photodiode line. Consequently, a resolution is deteriorated.